1. Field
The present disclosure relates generally to field scanning in which signals are transmitted at a number of frequencies in a test environment and signals, reflected in response to the transmitted signals, are received and analyzed. More particularly, the present disclosure relates to determining frequency characteristics of a test environment and supporting, moving, and determining the location of a transmitter and a receiver in a test environment for field scanning to reduce undesired effects on the transmitted and received signals in the test environment.
2. Background
Field scanning involves the transmission of signals at a number of frequencies in a test environment. The test environment may include either an open or enclosed space into which the signals are transmitted. The transmitted signals are reflected from the test environment and objects in the test environment. The reflected signals are received and may be analyzed to determine frequency-related characteristics of the test environment or of objects placed in the test environment.
Signals may be transmitted in the test environment at a number of frequencies. The frequencies of the signals transmitted in the test environment may depend on the particular test or analysis to be performed. For example, without limitation, the signals transmitted in the test environment may include radio frequency signals, radar cross section frequency signals, or signals at any other number of frequencies, ranges of frequencies, or combinations of frequencies.
Field scanning may be used for a number of purposes, objects, or applications. For example, field scanning may be used to identify frequency signatures of various objects. For example, without limitation, field scanning may be used to identify frequency signatures of vehicles, such as aircraft or other vehicles. Further, field scanning may be used to identify frequency responses of air traffic control towers or other airfield structures and operations to identify ambient signals at various frequencies. For example, without limitation, such ambient signals may include emissions from construction crew radios or from various field operation devices, such as aircraft maintenance devices, aircraft radios, nearby cellular telephone towers, amateur and saboteur radio transmissions, or other sources or combinations of sources of potential ambient signals that may affect air traffic control tower and air field operations. Field scanning also may be used to obtain frequency field test data for maritime, ground surveillance, police, mobile radio and telephone, global positioning system, and other electromagnetic products and services.
Field scanning methods and systems may be designed specifically for the test environment and the tests to be performed. Typically, a test environment for field scanning may include a transmitter and receiver, a reflector, an object under test, and a number of support structures. For example, a support structure may be used to support the object under test in the test environment during scanning. A typical structure for supporting the object under test may include a mounting base and pylon or other structures and combinations of structures for supporting the object under test at a desired position in the test environment. The object under test may be mounted to the support structure via a mechanism that provides for rotation or other movement of the test object with respect to the support structure.
The transmitter and receiver typically also may be mounted on a support structure in the test environment. For example, the transmitter and receiver may be mounted at the top of a pylon or other support structure that is positioned at a pre-determined location in the test environment. The transmitter and receiver may be attached to the pylon or other support structure via a mechanism that provides for rotation or other movement of the transmitter and receiver with respect to the pylon or other support structure. The transmitter and receiver may be mounted to the support structure facing the reflector.
During the performance of a field scanning test, the transmitter is controlled to emit signals at a number of frequencies in the direction of the reflector. The reflector reflects the transmitted frequencies back to the receiver. The reflected signals are received by the receiver. Frequency data derived from the received reflected signals may be recorded and analyzed.
Various objects in the test environment, including the various structures for supporting the transmitter and receiver in the test environment, may reflect and absorb signals at various frequencies and to various degrees. Therefore, such structures may affect the signals that are transmitted and reflected in the test environment in undesired ways. For example, the presence of such structures and other objects in the test environment may distort the frequency data obtained during a test. This distortion may reduce the accuracy of the frequency data collected and affect the analysis of such data in undesired ways unless such distortion can be corrected. Unless such distortion is identified and removed or accounted for in resulting test data, the actual frequency response of a vehicle or environment undergoing testing in the test environment may be determined less accurately.
The accuracy of frequency response measurements also may be affected by ambient emissions in the test environment where the measurements are made. For example, such ambient emissions may result from terrestrial radio frequency communications in the area where the frequency data is obtained.
Ambient emissions may affect any test or measurement in which a test signal is intentionally transmitted from a transmitter and a resulting test signal received by a receiver is analyzed. In any such test, signals from ambient emissions may be received by the receiver along with reflections of the intentionally transmitted test signal. In this case, the ambient emissions may mask or distort the reflections of the test signal generated by the transmitter. The test signal data derived from the signals received by the receiver may include data resulting from received ambient emissions, thereby affecting the analysis of the test signal data in undesired ways. Therefore, a reliable analysis of the received test signal data may not be made if the test is performed in the presence of ambient emissions.
The effect of ambient emissions on frequency field scanning and other tests involving transmitting and receiving a test signal may be reduced by conducting the tests or other measurements in an area where ambient emissions are known to be at a reduced level. However, conducting such measurements or other tests under such controlled conditions may be expensive, inconvenient, time-consuming, or impractical in many cases.
Accordingly, it would be desirable to have a method and apparatus that takes into account one or more of the issues discussed above, as well as possibly other issues. For example, it would be desirable to have a method and apparatus for identifying a baseline frequency response of a test environment for frequency field scanning. The identified baseline frequency response may take into account the frequency characteristics of ambient objects and signals in the test environment. Baseline frequency response data for the test environment may be used to improve the accuracy of any frequency field scanning tests performed in the test environment.